package caltriangle;
import java.util.Scanner;

//哈哈新成员快提交试试看！
public class Main {
	public static double area(double a,double b,double c) {
		double p=(a+b+c)/2.0;
		double s=p*(p-a)*(p-b)*(p-c);
		return Math.sqrt(s);
	}
	public static void main(String []arg) {
		Scanner input=new Scanner(System.in);
		double a,b,c;
		System.out.println("�����������ε������߳���");
		a=input.nextDouble();
		b=input.nextDouble();
		c=input.nextDouble();
		input.close();
		if(a+b<=c||a+c<=b||b+c<=a) System.out.println("���������Σ�");
		else{
			double s=area(a,b,c);
			System.out.println(s);
		}
	}
}
